This invention relates to coated articles including a layer structure of barrier/metal(or mostly metal)/barrier, and a method of making the same. This layer structure may be used by itself, or more preferably as only a component of an overall coating or layer system. In certain embodiments, a single sputtering target (e.g., cathode target) is used to make this layer structure. In these and/or other embodiments of the invention, the resulting coated article has approximately the same color characteristics as viewed by the naked eye before and after heat treatment (e.g., thermal tempering). Such coated articles may be used in insulating glass (IG) window units, vehicle windows, and/or other suitable applications.
The need for color matchability of coated articles (before heat treatment vs. after heat treatment) is known. Glass substrates are often produced in large quantities and cut to size in order to fulfill the needs of a particular situation such as a new multi-window and door office building, vehicle window needs, etc. It is often desirable in such applications that some of the windows and/or doors be heat-treated (i.e., tempered, heat strengthened or bent), while others need not be. Office buildings typically employ IG units and/or laminates for safety and/or thermal control. It is desirable that the units and/or laminates which are heat treated (HT) substantially match their non-heat treated counterparts (e.g., with regard to color, reflectance, and/or the like) for architectural and/or aesthetic purposes.
U.S. Pat. No. 5,376,455 discloses a coated article including: glass/Si3N4/NiCr/Ag/NiCr/Si3N4. Unfortunately, the coating system of the ""455 patent is not sufficiently color matchable after heat treatment with its non-heat-treated counterpart. In other words, the coating system of the ""455 patent has a rather high xcex94E value. This means that, unfortunately, two different coated articles with different coatings (one to be heat treated, the other not to be) must be made for customers who want their heat-treated and non-heat-treated coated articles to approximately match colorwise as viewed by the naked eye.
As with the ""455 patent, it has mostly been possible to achieve matchability only by providing two different layer systems, one of which is heat treated (HT) and the other is not. The necessity of developing and using two different layer systems to achieve matchability creates additional manufacturing expense and inventory needs which are undesirable.
However, commonly owned U.S. Pat. No. 5,688,585 discloses a solar control coated article including glass/Si3N4/NiCr/Si3N4, wherein matchability is achieved with a single layer system. An object of the ""585 patent is to provide a sputter coated layer system that after heat treatment is matchable colorwise with its non-heat-treated counterpart. However, the ""585 patent uses a heat treatment (HT) of only three (3) minutes (col. 10, line 55). Longer heat treatments are often desired in order to attain better tempering or HT characteristics. Unfortunately, it has been found that with longer HT times the coatings of the ""585 patent cannot maintain low xcex94E values and thus lose color matchability. In particular, it has been found that in coatings such as those of the ""585 patent, xcex94E values jump significantly upward after HT for 4-5 minutes at a temperature of from about 600 to 800 degrees C.
Consider the following layer stack (see Comparative Example below): glass/Si3N4/NiCr/Si3N4, where the underlayer of Si3N4 is about 50-70 xc3x85 (angstroms) thick, the NiCr layer is about 325 xc3x85 thick, and the overcoat of Si3N4 is about 210-310 xc3x85 thick. As explained in the Comparative Example below, this coated article has a rather high transmissive xcex94E* value of about 5.9 after heat treatment (HT) at 625 degrees C for ten (10) minutes. This high transmissive xcex94E value means that a HT version of the ""585 coated article does not approximately match colorwise non-heat-treated counterpart versions with regard to transmissive color after 10 minutes of HT.
The following Comparative Example layer system was provided on about a 6.0 mm thick clear soda-lime-silica glass substrate 1, and was: silicon nitride/NiCr/silicon nitride. A Leybold Terra-G six-chamber sputter coating apparatus was used to sputter the coating onto the glass substrate. Five cathodes were in each chamber, so there were a total of 30 cathode targets in the sputter coater (not all were used). Cathode numbering utilizes the first digit to refer to the coater chamber, and the second digit to refer to the cathode position in that chamber. For example, cathode #42 was the second cathode (second digit) in the fourth (first digit) sputter chamber. Cathode #s 42, 55 and 61 were dual C-Mag type cathodes; and cathode #s 44 and 45 were planar cathodes. Below, xe2x80x9c*xe2x80x9d means Al content of approximately 10%. The line speed was 3.5 meters per minute (m/min.). All gas flows (i.e., Ar and N) are presented in units of sccm. Voltage is measured in terms of volts, and frequency in terms of kHz. Pressure is measured in hPa, and power in kW. T-gas refers to trim (or tuning) gas used to individually adjust gas flows along cathode length to make corrections regarding layer thickness uniformity (all T-gas was at 100 sccm). C % refers to the percentage (%) of trim gas introduced at the center, while PS % refers to the percentage of the trim gas introduced at the pump side, and VS % refers to the percentage of the trim or tuning gas introduced at the viewer side. The NiCr targets were approximately 80/120 NiCr.
After being sputtered onto glass substrate 1 as set forth above, the resulting coated article of the Comparative Example was tested and found to have the following characteristics monolithically (not in an IG unit), where the heat treatment (HT) involved heating the monolithic product at about 625 degrees C for about 10 minutes. It is noted that a* and b* color coordinate values are in accordance with CIE LAB 1976, Ill. C 2 degree observer technique, and xcex94a* and xcex94b* are in terms of absolute value. Moreover, sheet resistance (Rs) is in units of ohms per square as is known in the art.
As can be seen above, the Comparative Example experienced a rather high transmissive xcex94E* value of 5.9 and a rather high film side reflective xcex94E* value of 6.86 (evidencing that the coating is not color stable upon HT). It is believed that these high xcex94E* value(s) associated with the coating of the Comparative Example are caused for at least the following reasons. Prior to heat treatment (HT), the vast majority of the Ni is located in the NiCr layer and the vast majority of the Si and N from the upper Si3N4 layer is located in that upper layer. However, when the Comparative Example coated article is heat treated (HT) as discussed above, a significant portion of the Ni from the NiCr layer migrates (of diffuses) into the upper Si3N4 layer (see parent application). Additionally, upon HT a significant portion of the Si and N from the upper Si3N4 layer migrate(s) into the NiCr layer. In other words, the interface between the metal NiCr layer and the upper dielectric Si3N4 layer becomes blurred and non-distinct due to HT.
Unfortunately, the aforesaid migrations of the Si, N, and Ni from their pre-HT positions to their post-HT positions (due to HT) causes significant color shifting to occur and thus explains the large xcex94E* value(s) associated with the Comparative Example.
In view of the above, it will be apparent to those skilled in the art that there exists a need for a coating or layer system that has a low xcex94E (or xcex94E*) value(s) and thus good color matchability characteristics after heat treatment (HT). It is a purpose of this invention to fulfill the above-listed need, and/or other needs which will become more apparent to the skilled artisan once given the following disclosure.
An attempt has been made to overcome the aforesaid problem with the aforesaid silicon nitride/NiCr/silicon nitride layer system (see Comparative Example) by nitriding the NiCr layer. While this significantly reduces color shift upon HT and is thus desirable in certain embodiments of this invention, it can reduce the deposition rate of the NiCr layer (e.g., by 20% or so). Moreover, this latter technique of simply nitriding the NiCr layer tends to reduce the metallic nature of the central NiCr layer thereby leading to a less sharp appearance of the resulting coated article.
In the parent application, a barrier layer (e.g., NiCrOx) is introduced between the silicon nitride layer and the NiCr layer, on one or both sides of the NiCr layer. As will be appreciated by those skilled in the art, the term NiCrOx as used herein means that the Ni and/or Cr may be at least partially oxided. This NiCrOx barrier layer, which is at least partially oxidized/oxided, enables color shift upon HT to be significantly reduced thereby rendering this approach acceptable in certain embodiments of the instant invention. Color shift upon HT is reduced (i.e., xcex94E* is lowered) because the barrier layer reduces interdiffusion of Ni and the like from occurring upon HT, so that the metallic nature of the NiCr is better preserved. The provision of this oxide barrier layer also improves corrosion resistance. However, this approach requires a three layer stack (i.e., NiCrOx/NiCr/NiCrOx) to replace a single layer (i.e., NiCr), so that two additional cathodes (or targets are required). Thus, while this approach is acceptable according to certain embodiments of this invention, it does require additional cathodes/targets and thus can be improved upon as discussed below.
An object of this invention is to provide a coating or layer system that has good color stability (i.e., a low xcex94E* value(s)) with heat treatment (HT).
Another object of this invention is to provide a coating or layer system having a xcex94E* value(s) (e.g., transmissive and/or glass side reflective) no greater than 5.0 upon heat treatment (HT). Such HT may be, for example and without limitation, at a temperature of at least about 580 or 600 degrees C for a period of time of at least 5 minutes (more preferably at least 7 minutes, and most preferably at least 9 minutes).
Another object of this invention is to provide a diffusion/migration prevention layer or layer portion (i.e., anti-migration layer or layer portion) between a dielectric layer (e.g., silicon nitride) and a solar control layer or layer portion (e.g., NiCr) in order to reduce elemental migration and improve color stability upon HT so as to enable the resulting coated article to have low xcex94E value(s). The anti-migration layer or layer portion may include chromium oxide, NiCrOx, and/or any other suitable material such as another metal oxide.
Another object of this invention is to sputter coat a layer structure including metal oxide/metal/metal oxide using a single sputtering target or cathode.
Another object of this invention is to sputter coat a layer structure including NiCrOx/NiCr/NiCrOx using a single sputtering target or cathode. This layer structure is thus part of the same layer (which is oxided/oxidized differently at different portions thereof) in certain embodiments of this invention. In certain optional embodiments of this invention, this layer structure may also be at least partially nitrided.
Another object of this invention is to fulfill one or more of the above-listed objects and/or needs.
According to certain example embodiments of this invention, by at least forming an anti-migration layer or layer portion between a solar control layer or layer portion and a dielectric layer, migration of N, Cr, and/or Ni (or other relevant material(s) depending upon the materials used for the dielectric and solar control layers) can be reduced during HT thereby enabling the resulting coated article to be more color-stable with HT (i.e., have lower xcex94E* value(s)). Less element migration during HT results in better color stability upon HT, and thus lower xcex94E* value(s). In embodiments where the anti-migration layer or layer portion(s) is/are deposited using the same target as is used to deposit the solar control layer or layer portion, hardware and thus cost/time can be reduced.
In certain example embodiments of this invention, one or more of the above-listed objects and/or needs is fulfilled by providing a coated article comprising: first and second dielectric layers supported by a substrate; a layer structure provided between the first and second dielectric layers, said layer structure including an at least partially oxidized top layer portion, a central layer portion and an at least partially oxidized bottom layer portion, wherein the central layer portion is more metallic than the top and bottom layer portions; and wherein the coated article has a transmissive xcex94E* value no greater than 5.0 upon heat treatment. The central layer portion may or may not contact the top/bottom layer portions in different embodiments (i.e., further oxidation grading may take place therebetween).
In certain other embodiments of this invention, one or more of the above-listed objects and/or needs may be fulfilled by providing a coated article comprising: first and second dielectric layers supported by a substrate; an oxidation graded layer located between the first and second dielectric layers, the oxidation graded layer having a top side and a bottom side; and wherein the oxidation graded layer is oxidation graded to become gradually less oxidized from the bottom side of the layer to a central portion of the layer and then to become gradually more oxidized from the central portion of the layer to the top side of the layer.
In certain other embodiments of this invention, one or more of the above-listed objects and/or needs may be fulfilled by providing a method of making a coated article, the method comprising: providing a sputtering target comprising at least one metal; sputtering a layer structure on a substrate using the target; and wherein the sputtering includes using from 0.1 to 4.0 sccm oxygen gas per kW power (sccm/kW) so that the resulting layer structure from using the target is oxidation graded to include top and bottom portions which are more oxidized than a central portion.
This invention will now be described with respect to certain embodiments thereof as illustrated in the following drawings, wherein: